Neurocutaneous melanosis, better referred to as neurocutaneous melanocytosis (NCM), is a rare congenital disorder occurring in childhood characterized by proliferation of melanocytes in the central nervous system (CNS), associated with large congenital melanocytic nevi. The phenotype of the CNS lesions varies, ranging from that of a benign, nevuslike lesion, to one of an aggressive-looking, atypical cell proliferation; however, specific diagnostic criteria allow the distinction from CNS metastasis of a primary skin melanoma. NCM can present with severe neurologic manifestations, and usually has a relentless clinical progression whence neurologic symptoms appear. Dissemination to the peritoneal surface by ventriculo-peritoneal shunting has been exceptionally observed, and we describe 2 cases of such occurrence, one of which was associated with a "bulky perineal nevocytoma" with complex cytogenetic rearrangements. This "metastatic" spreading supports an aggressive phenotype, able to seed and establish new colonies, although only after facilitated translocation of the proliferating cells through the shunt conduit; the aggressiveness of these lesions in our cases is further supported by the histopathologic features and clinical course. The biologic features of NCM cells merit further exploration, as they may shed light on a much more frequent neoplastic neurocristopathy, namely, malignant melanoma.